In a waterproof case with a waterproof structure disclosed in JP-A-11-111381, a cover is provided with a filter fitting part. This filter fitting part is provided with a filter breathing hole, a filter welding surface to which a filter is welded and which is formed so as to surround the periphery of this filter breathing hole, and a projection for forming the filter fixing part. A water-repellent filter is placed on the filter welding surface and is rounded inside while the projection is melted to form the filer fixing part, thereby being fixed.
As described above, by providing the filter breathing hole formed in the cover with the water-repellent filter, it is possible to hold the waterproofness of the case and to circulate air between the inside and the outside of the case. However, in the waterproof case described in JP-A-11-111381, there is a possibility that when the case is covered with water, water will be collected in a depression formed by the water-repellent filter and the filter fixing part. In a state where water is collected in the depression in this manner, there is a possibility that water will soak into the water-repellent filter, thereby the water may enter into the inside of the waterproof case. Moreover, when the filter breathing hole is closed with water and the inside or outside temperature of the case is changed, the inside of the case may be brought into a negative pressure so as to cause water to be drawn into the case.